Nonwoven moldable composite

ABSTRACT

A heat stabilized, moldable, consolidated nonwoven panel resistant to shrinkage when molded during a subsequent thermoforming operation, said panel being substantially stiff and comprised of a nonwoven structure of reinforcement fibers admixed throughout and encapsulated by a thermoplastic resin formed from melted and compressed thermoplastic fibers having a melting point less than the melting point of said reinforcement fibers, said reinforcement fibers comprising 60-20 percent per volume of said panel and having a length of from 1-6 inches sufficient to enable said panel to achieve at least about 50 percent elongation during thermoforming.

This is a division of prior application Ser. No. 07/880,624 filed May8,1992, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to nonwoven composite materialsand, more particularly, to nonwoven fibrous panels adapted forthermoforming. Specifically, the present invention relates to nonwovenmoldable composite materials having enhanced stiffness/weight ratios andenhanced resistance to shrinkage during thermoforming and their methodsof manufacture.

2. Description of the Prior Art

Nonwoven needlepunch fiber technology has been utilized in the past in avariety of manners to form a diverse number of nonwoven flexible fabricmaterials and products. Examples of such technology for producingflexible nonwoven materials include U.S. Pat. No. 4,420,167, No.4,258,094, No. 4,581,272, No. 4,668,562, No. 4,195,112, No. 4,342,813,No. 4,324,752, No. 4,315,965, No. 4,780,359, and No. 5,077,874.

In certain applications, however, flexible nonwoven materials havingfabric-like surfaces are not the most desired product. In fact, thereare certain instances where a more rigid nonwoven material is desirable,for example for use as a trunkliner to protect electronic componentslocated in the trunk area. In certain past situations, plastics havebeen utilized for such applications. Historically, plastic compositepanels have been manufactured using any number of different techniques.In the case of panels or materials suitable for low pressurethermoforming, which is desirable for trunkliner applications and othersimilar type of applications requiring molding, several processes havebeen utilized.

One typical process of the prior art is based on paper makingtechnology. In this instance, short staple fiber reinforcementmaterials, having fiber lengths typically less than one inch, are mixedwith a desired resin system, disbursed in a slurry, applied onto aporous belt, dried, and then consolidated using heat and pressure. Inthis instance, the desired resin system has been either a resin emulsionor additional fibrous materials of a lower melting point.

Other prior art processes rely on extrusion techniques to form a melt ofthe desired resin, which may or may not contain short staple fiberreinforcement materials and/or fillers. Panels are then formed bydirecting the molten resin through a slot die. One variation of thisprocess uses a resin sheet which is combined with premanufacturedreinforcement webs shortly after the extrusion die. These materials maybe made in a sandwiched construction of resin-reinforcement-resin, andthen consolidated through a compression operation consisting of highpressure rollers or presses.

In yet another prior art process, which has been used extensively forlight weight textile type products such as diaper linings, interlinings,and the like, includes forming a nonwoven structure through a textileprocess such as carding or airlay technology of primarily reinforcementfibers. These reinforcement fibers can contain lower melting binderfibers. This nonwoven structure is then exposed to heat and pressure toform a fibrous nonwoven structure containing bond points in thestructure. This is not unlike flexible textile manufacturing processesdescribed in some of the aforementioned patents. Alternatively, thenonwoven structure may be exposed to resin systems via a spray or dipapplication of resin emulsions, which are then dried by way of heatand/or pressure.

Some of the drawbacks of the textile based technology discussed above,however, include the fact that if additional decorative or reinforcementmaterials such as carpeting or the like needs to be adhered or connectedto the composite substrate material, such additional material hastraditionally been needlepunched to attach it to the composite materialsalready formed. Such needlepunching has been shown to change theappearance of the decorative material or weaken the reinforcementmaterials. In the alternative, such carpeting or other decorative layercan be separately adhered to the composite substrate by use of separateadhesive applications.

Moreover, such composite materials of the past have exhibited a certainamount of shrinkage when subsequently exposed to additional heat duringthermoforming processes to mold the composite into a desired shape forapplication as a trunkliner, dash panel or any other type of part. Suchshrinkage during thermoforming can cause missizing of the desiredcomponent part. Alternatively, it requires precise prediction withrespect to the amount of shrinkage in order to incorporate suchshrinkage into the original panel size prior to thermoforming. Yetanother alternative includes oversizing the panel so as to insure thatshrinkage occurring through thermoforming would not affect the desiredend product size. However, excess material must be trimmed off, and thisis unnecessary waste. Therefore, there remains a need for a stiff, lessflexible nonwoven composite material which is capable of beingthermoformed and molded without shrinkage as well as providing alternateattachment mechanisms for decorative or reinforcement materials.

SUMMARY OF THE INVENTION

In one aspect of the invention there is provided a heat stabilized,moldable, consolidated nonwoven panel resistant to shrinkage when moldedduring a subsequent thermoforming operation, the panel beingsubstantially stiff and comprised of a nonwoven substrate structure ofreinforcement fibers admixed throughout and encapsulated by athermoplastic resin formed from melted thermoplastic fibers having amelting point less than the melting point of said reinforcement fibers,the panel having assumed a densified structure resulting from saidthermoplastic resin having displaced, under compressive force, asubstantial amount of the air voids present in the nonwoven structurebefore having been subjected to such compressive force, saidreinforcement fibers comprising 60-20 percent per volume of said paneland having a length of 1-6 inches sufficient to enable said panel toachieve at least about 50 percent elongation during thermoforming.

In one embodiment the composite has an air void volume no greater thanapproximately 20 percent.

BRIEF DESCRIPTION OF THE DRAWING

The accompanying drawing, which is incorporated in and forms a part ofthe specification, illustrates a preferred embodiment of the presentinvention and together with a description, serves to explain theprinciples of the invention. In the drawing:

FIG. 1 is a schematic showing one embodiment of the process of thepresent invention used to form the material of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with the process of the present invention, at least twodifferent types of fibers are blended together in preparation for a battformation process. The base or first fiber is a reinforcement fiber,while the second fiber is thermoplastic in nature and will provide theresin utilized to bond the first reinforcement fibers together asdiscussed below.

The first type of fiber or reinforcement fiber may be thermoplastic,thermoset, inorganic or organic in nature as long as its melting pointexceeds that of the second or resin fibers. In the preferred embodiment,the first type of fiber is either a non-thermoplastic fiber or athermoplastic fiber having a melting point as explained above. Suitablenon-thermoplastic fibers available for use as a first type of fiberinclude, but are certainly not limited to, wool, cotton, acrylic,polybenzimidazole, aramid, rayon or other cellulosic materials, carbon,glass, and novoloid fibers. Due to their very high temperaturestability, for purposes of the present invention, polybenzimidazole havebeen characterized as non-thermoplastic. If the the first type of fibersin the preferred embodiment are thermoplastic, the thermoplasticmaterial must have a higher melting point temperature than the meltingpoint temperature of the second thermoplastic fibers so that the secondthermoplastic fibers may be melted without melting the first fibers. Ifthe first fibers are thermoplastic in nature, any of the thermoplasticsdescribed below as being available for use as the second fibers are alsoavailable for the first fibers so long as the consideration stated abovewith respect to melting point is met. If desired, the preferred nonwovenbatt may have components in addition to the above-described first andsecond type of fibers.

The second resin fiber may be made from any type of thermoplasticmaterial having appropriate melting points. In the preferred embodiment,such materials include, but are not limited to, polyethylene,polypropylene, polyester, nylon, polyphenylene sulfide, polyethersulfone, polyether-ether ketone, vinyon, as well as bicomponentthermoplastic fibers. In fact, bicomponent fibers may be utilized asboth first and second fibers. Such bicomponent fibers include a highermelting point core material surrounded by a lower melting point sheathmaterial. In this manner, as heat is applied and the temperatureincreased, the sheath material melts thereby exposing the higher meltingpoint core material which remains as the reinforcement fiber. An exampleof a usable bicomponent thermoplastic fiber is one made of apolypropylene core and a polyethylene sheath. Chisso Corporation ofJapan manufactures a suitable bicomponent polyolefin fiber sold as"Chisso ESC" fiber. In the most preferred embodiment, the firstreinforcement fiber is a higher melting point polyester while the secondthermoplastic resin fiber is a lower melting point polypropylene.

Referring now to FIG. 1, the first and second fibers described above areadmixed together and formed into a batt 10 by way of typical textileprocesses such as carding/crosslapping or an airlay process. Typically,the second thermoplastic fibers representing the resin component of theultimate composite will be utilized in the amount of 40-80 percent byvolume of the total blend. Likewise, the first fibers representingreinforcement fibers will typically represent 20-60 percent of theblend. In the most preferred embodiment, the mix is in the ratio of 65percent of the second resin fiber and 35 percent of the firstreinforcement fiber.

The fiber is then passed through a batt formation process in order toconsolidate the fibers and form a nonwoven web 12. Any type of battformation technique known to the art may be utilized in order to formthe batt 10. Examples of such techniques include carding/crosslappingoperations or an airlay operation. The preferred weight of the batt 10thus formed is about 300 g/m² or higher. In the preferred embodiment, aneedlepunching technique is utilized to consolidate the batt 10 to formthe nonwoven structure 12. Referring to FIG. 1, a needle loom 14 isillustrated as being utilized to consolidate the batt 10 into thenonwoven structure 12. The needle loom 14 includes needles 16 that punchinto and withdraw from the webbing at desired number of strokes perminute as more specifically described in U.S. Pat. No. 4,424,250, thecontents of which are specifically incorporated herein by reference.

It is important to note that the first reinforcement fibers of the batt10 are preferably of a long but discrete length, that is of a length of1-6 inches. This differentiates the ultimate composite 20 of the presentinvention from prior art types of composites, which includes thoseutilizing short staple fibers produced by wet-laid techniques or thelike, or those utilizing continuous fibers. By maintaining thereinforcement fibers within the length specified above, it wasdiscovered that the fibers help distribute forces encountered duringthermoform molding of the composite, thereby providing certainbeneficial elongation characteristics to the composite 20 of the presentinvention not available with prior art composite materials. This isdiscussed in greater detail below.

Returning to FIG. 1, the nonwoven structure 12 is heated above themelting point of the second thermoplastic fibers in order to melt thesecond fibers and encapsulate the first reinforcement fibers with resin.This is immediately followed by a compression operation. It wasdiscovered that if the nonwoven structure 12 is heated to melt thesecond thermoplastic fibers and then immediately compressed, the meltedthermoplastic fibers, or resin, becomes essentially liquid under thetemperature and pressure range developed and responds by flowingthroughout the web and displacing a substantial amount of the air voidspresent in the initial material. In fact, whereas prior art compositematerials include up to 85 percent air voids volume in the ultimatecomposite material, the process of the present invention creates acomposite 20 having encaptured air of 20 percent or less and, in themore preferred embodiment, air voids of only 10-15 percent and even lessthan 10 percent.

There are any number of ways known to the art of accomplishing heatingof the nonwoven structure 12 to achieve densification, and these includehot calendaring, heated flat platten pressing, continuous belt fedheating stations such as used in lamination or transfer printing, andthe like. A preferred method developed with the present inventioninvolves feeding the nonwoven structure 12 through an impingement orthrough-air heating unit 18. In order to raise the nonwoven structuretemperature above the melting point of the second thermoplastic fibers,hot air is preferably forced through the nonwoven structure by the unit18 so as to thoroughly heat the entire nonwoven structure throughout.This is as opposed to a radiant heating unit which tends to heat thesurface of the nonwoven structure to a much greater degree than theinterior portion of the nonwoven structure. Since a thoroughdistribution of melted resin is desired with the present invention, itis important that the nonwoven structure be heated thoroughlythroughout.

Immediately upon completion of the heating process by unit 18, theheated nonwoven structure with its melted thermoplastic resin isdirected through a compression stage wherein, as described above, theresin flows throughout the nonwoven structure encapsulating the firstreinforcement fibers and displacing the air voids therein. While anytype of compression technique known to the art may be utilized with themethod of the invention, the preferred embodiment utilizes a pair ofpinch rollers 22, 24 which are maintained preferably at a temperaturebelow the melting point of the resin so as to assist in cooling of theresin. The rollers 22, 24 are spaced with an appropriate gap so as todevelop sufficient closure pressure at the nip 28 to cause the mobilemolten resin in the nonwoven structure to redistribute within the matrixof the reinforcement fibers therein. Upon compression caused by therollers 22, 24, the nonwoven structure is cooled to form the compositematerial 20. As described above, the rollers 22, 24 may assist in theinitial cooling by being maintained at an appropriate lower temperature.

It is frequently desirable to utilize the composite material 20 as asubstrate and add to it decorative or reinforcement covering materials.Prior to the present invention, such materials were attached to acomposite formed from textile processes either by a needlepunchingprocess, which tends to change the decoration materials appearance orweaken the reinforcing material, or by adding an additional adhesive,which added weight and required an additional processing step. With thepresent invention, a covering material 26 may be attached to thecomposite 20 by introducing the material 26 on either one 25 or bothsides 25, 27 of the heated nonwoven structure at the nip point 28 toyield a finished composite material 30 having the covering material 26attached thereto. The covering material 26 is attached to the composite20 by compressing the covering material 26 against the surface 25 of theheated nonwoven structure so that the resin from the heated nonwovenstructure penetrates the covering material 26 and thereby binds thecovering material 26 to the substrate 12. Thus, the resin within thenonwoven structure also acts as the adhesive to attach the covermaterial 26 to the nonwoven structure to provide the final compositeproduct 30. In the case of a decorative material, virtually any chemicaltype may be utilized as the covering material 26 so long as its meltingpoint is greater than or equal to the melting point of the secondthermoplastic fibers. While FIG. 1 only illustrates the attachment ofthe cover material 26 to one side 25 of the-nonwoven structure, it is tobe understood that both sides 25, 27 of the nonwoven structure can becovered by a material 26 simultaneously by introducing another coveringmaterial at the nip point 28 from the other side 27 of the nonwovenstructure. The covering material 26 can be of any type of material suchas textile, ie., carpets, cloths and the like, or other types ofmaterials such as films, foils, spunbonded reinforcement materials andthe like.

Since the resin system of the composite material 20 has beenrepositioned during its mobile or heated phase by the compressionprocess, the resulting composite 20 is essentially free of trapped airas described above. In addition, essentially 100 percent contact existsbetween the resin system of the composite 20 and the first reinforcementfibers therein. Moreover, the final composite product 30 having acovering layer attached thereto is a singular material wherein thecovering material 26 is intimately bound to the composite 20 byutilizing the same resin system that binds the fibers of the composite20 together to bind the covering material 26 to the composite 20. Thisresults in a product with performance properties similar to the extrudedresin with reinforcement fibers in terms of offering a very highstiffness to weight ratio, while maintaining sufficient ultimateelongation to allow reliable thermoforming into complex shapes asdescribed below.

As a result of the aforementioned processing, the resulting compositematerial 20 is a moldable, nonwoven composite. Due to the heating andcompressing which densifies the material 20, the resultant composite 20is highly resistant to shrinkage during subsequent thermoformingprocesses. The composite 20 ends up being a nonwoven structure of thefirst reinforcement fibers which are thoroughly mixed throughout andencapsulated entirely by the resin formed from the second melted fibers,the composite having an air volume of 20 percent or less and preferablyin the range of 10-15 percent. Thus, substantially all of the air voidsin the initial batt 10 have been displaced and removed.

The composite material 20 with or without covering material 26 may beutilized in a wide variety of applications as previously mentioned. Withrespect to thermoforming, the composite 20 has achieved elongation atfailure values in excess of 50 percent elongation under thermoformingconditions. In other words, the composite 20 of the present invention isable to achieve in excess of 50 percent elongation during thermoformmolding without cracking or failing. This makes the composite materialof the present invention highly suitable for any method of shaping partsrequiring heating or thermoforming techniques.

The process and product of the present invention described above differsignificantly from prior art processes and products in that exclusivelydry laid nonwoven structure forming technology is utilized as opposed towet laid technology of many of the prior art products. The resultantcomposite structure of the invention comprises a matrix of reinforcementfibers essentially surrounded by resin material and essentially free ofair spaces, which provides a very dense, stiff, yet lighter weightmaterial. Nonetheless, this material is highly elongatable forthermoforming capabilities. Moreover, the material of the presentinvention allows lamination of decorative or additional reinforcementmaterials without the use of additional adhesive and without the use ofneedlepunching or other similar type of techniques which tend to damagethe reinforcement material or change the appearance of the decorativematerial. As a result, a stiff, lighter-weight composite material isachievable with the present invention without being brittle, and yet isvery compliant under thermoforming processes. This produces a compositematerial that is capable of being utilized in a wide variety ofapplications with significant advantages over existing nonwovencomposites.

The foregoing description and the illustrative embodiments of thepresent invention have been shown in the drawing and described in detailin varying modifications and alternate embodiments. It should beunderstood, however, that the foregoing description of the invention isexemplary only, and that the scope of the invention is to be limitedonly to the claims as interpreted in view of the prior art. Moreover,the invention illustratively disclosed herein suitably may be practicedin the absence of any element which is not specifically disclosedherein.

The embodiments in which an exclusive property or privilege is claimedare defined as follows:
 1. A heat stabilized, moldable, consolidatednonwoven panel having an air void volume of at least about 10 percentand resistant to shrinkage when molded during a subsequent thermoformingoperation, said panel being formed of at least one layer, and beingsubstantially stiff and comprised of a nonwoven substrate structure ofreinforcement fibers admixed throughout and encapsulated by athermoplastic resin formed from melted thermoplastic fibers having amelting point less than the melting point of said reinforcement fibers,said panel having assumed a densified structure resulting from saidthermoplastic resin having displaced, under compressive force, asubstantial amount of the air voids present in the nonwoven substratestructure before having been subjected to such compressive force, saidthermoplastic resin comprising 40-80 percent per volume of said panelbased on the total blend of reinforcement fibers plus thermoplasticresin in the panel, and said reinforcement fibers comprising 60-20percent per volume of said panel based on the total blend ofreinforcement fibers plus thermoplastic resin in the panel, and thereinforcement fibers having a length of from 1-6 inches sufficient toenable said panel to achieve at least about 50 percent elongation duringthermoforming.
 2. The panel of claim 1 having an air void volume nogreater than about 20 percent.
 3. The panel of claim 1 having an airvoid volume of substantially less than 85 percent.
 4. The panel of claim1 which has been molded by thermoforming to form a shaped, substantiallystiff thermoformed article in which at least about 50 percent elongationhas been achieved as a result of molding.
 5. The panel as claimed inclaim 1, wherein said reinforcement fibers comprise at least one type ofnon-thermoplastic fibers selected from the group consisting of fibers ofwool, cotton, acrylics, polybenzimidazoles, aramids, rayon, carbon,glass, and novoloids.
 6. The panel as claimed in claim 1, wherein saidthermoplastic fibers forming said resin comprise at least one type ofthermoplastic fiber selected from the group consisting of fibers ofpolyethylene, polypropylene, polyester, nylons, polyphenylene sulfides,polyether sulfones, polyether-ether ketones, vinyon, and bicomponentthermoplastic fibers.
 7. The panel as claimed in claim 1, wherein saidreinforcement fibers comprise polyester, and said resin formingthermoplastic fibers comprise polypropylene.
 8. The panel as claimed inclaim 1, wherein said reinforcement fibers comprise approximately 35percent by volume of said blend while said resin comprises approximately65 percent by volume of said blend.
 9. The panel as claimed in claim 1,wherein said panel further includes a covering member attached to atleast one surface thereof utilizing the thermoplastic resin of saidsubstrate structure, the covering member becoming attached bycompressing the covering member against the substrate structure so thatthe thermoplastic resin penetrates the covering member and binds it tothe substrate structure upon subsequent cooling and resolidifying. 10.The panel as claimed in claim 1, wherein said covering member is securedto both sides of said material.
 11. The panel as claimed in claim 1,wherein said covering member attached to said material comprisescarpeting.
 12. The panel of claim 9 which has been molded bythermoforming to form a shaped, substantially stiff thermoformed articlein which at least about 50 percent elongation has been achieved as aresult of molding.